My two pennies on what-is and how-to value Social Networking for clients when asked by a friend yesterday—————–
Well, I think to put hard numbers on it requires that you already have your metrics in place. Like, if you knew how much $ you made in sales when spamming (I mean emailing) your database, you could figure out how much each name on the db was worth. Double that list and it seems reasonable to expect a doubling of your sales.

Same thing for the website–if you have Analytics installed, you should know your conversion rate. It should also hold that the value to you of website traffic is Visits X Conversion rate.

Alot of Social Networking is also a branding exercise, not just advertising. What is the value of perpetuating your brand to your audience and providing an authentic voice that humanizes your company in real time with your audience? I don’t know how to put a number on that of course, but it DOES seem valuable, no? Does Tony Hawk become more relevant to his fan base when he talks about his latest exhibition or when he gives away gear? Is it cool when he mentions your name as a winner of some prize? Probably, yeah.

It depends on your company too. Take Wired magazine–they have a twitter feed but they don’t make any money directly from it. If the Wired twitter-er puts out some good content, fans follow the link to their site, read/watch whatever and maybe later subscribe to the print version.

Also, it depends on what your objective is and how you use those tools. You can drive sales, you can do PR, you can “brand” if that’s a verb. Look at PDL’s facebook page. On all my emails now I have facebook.pdxdesignlab.com as a subdomain in my email signature. It’s another portfolio for me. Of course you know how much work you’d get as a design company if you didn’t have a website–ZERO. What is the value of that website? Don’t know, but I know what it would be if you didn’t have one.

Advertising as you pointed out, can be tracked very well. You can see how your campaigns are performing and see how changes are reflected in sales. But it definitely is squishier with SN as a whole.